The invention is directed to a method for structuring a copper and/or permalloy layer on a substrate surface by means of dry etching by use of a metallic mask applied to the layer to be structured, this mask in turn carrying a photoresist layer that reproduces the geometry of the structure. The field of application of such a method is the general production of structured copper layers on electronic modules. In particular, however, it can also be employed in the manufacture of thin-film magnetic heads.
As a consequence of its very good electrical conductivity, copper is used to a great extent as a conductor track material in the manufacture of conductive connections on module substrates, PC cards, etc., and is nearly exclusively used in technology for thin-film magnetic heads. The conductive structures are usually produced in a photolithographic manner. A pattern of a photoresist layer corresponding to the desired conductive connections is first produced on a copper layer that is applied to a substrate surface. On the basis of a method that is still largely wet-chemical at present, the copper regions that are not protected by the photoresist are selectively etched out from the copper layer. Only the pattern of the conductive connections then remains on the substrate surface.
Steep etching edges, however, can not be achieved in practice with the known wet-chemical methods. Given progressive miniaturization of electronic circuits and also given increased numbers of turns in thin-film magnetic heads, it is therefore becoming increasingly more difficult to generate conductive patterns having the desired precision in a wet-chemical manner. Also, contaminants can be deposited on the parts to be etched from the etching baths themselves. These contaminations are less and less tolerable because of increasing miniaturization.
A different structuring method is employed in a wet chemical method. A titanium mask is first produced. The production of the actual copper structure in an ion beam etching process follows. The disadvantages of the wet-chemical method, however, can also be recognized on the finished copper structure given such a half wet and half dry structuring.
There have therefore been no lack of attempts to create usable copper structures with the assistance of exclusive dry etching processes. Thus, for example, the publication "Surface Texturing of Copper by Sputter Etching With Applications for Solar Selective Absorbing Surfaces" in the Journal of Vacuum Science Technology, Volume 17 (6), Nov./Dec. 1980, pages 1170 ff incorporated herein, discloses an attempt to erode copper by use of cathode sputtering in an argon atmosphere. The publication EP-A No. 0 133 621 corresponding to U.S. Pat. No. 4,557,796 incorporated herein, also discloses a method wherein copper is to be etched in dry fashion in a glow discharge that contains compounds having at least one methyl or methylene group. What is especially disturbing when etching with cathode sputtering, however, is that the eroded material is partly re-deposited onto the surfaces to be etched. Dry etching in a methyl atmosphere has not yet been able to become standard practice.
There have also been attempts to structure copper by plasma etching and by reactive ion etching. Halogen compounds are thus utilized as an etching reactant. Given copper, however, there is the difficulty that its halogen compounds do not become volatile until relatively high temperatures. Thus, the volatility temperature in a plasma etching process for copper, wherein the etching reactant is composed of iodine which forms copper iodide together with the copper, amounts to 500.degree. C. and above.
EP-A No. 0 054 663 incorporated herein also discloses a method for etching copper with the assistance of reactive ion etching in an atmosphere containing carbon tetrachloride and alcohol. In this process, however, the organic polymers that are used as masks degrade.
Similar difficulties are presented in the previously disclosed methods for structuring permalloy that is particularly employed in the manufacture of thin-film magnetic heads. Two methods, a wet-chemical method and a dry structuring method with the assistance of four masks, are predominantly employed here. The wet-chemical method for structuring permalloy corresponds to the above-described method for structuring copper. The unprotected permalloy surface regions are etched away in an etching bath with the assistance of a photoresist mask that protects the permalloy layer lying therebelow. The significant disadvantage of this method lies in the uncleanness of all etched edges and in the angularity. Given thick structures of modern thin-film magnetic heads, this angularity lies on the order of magnitude of less than 45.degree.. Such acute edges, however, lead to a low degree of neighboring track attenuation at the finished magnetic head. This is to be attributed to the acute edges acting like antennas on magnetic fields, and a high susceptibility to disturbance therefore results when recording and playing back electrical signals on magnetic discs.
The trend toward higher storage densities on magnetic discs, however, is continuing. Narrower and narrower tracks are being recorded on the magnetic discs. Furthermore, the tracks themselves are being placed closer and closer together. It therefore becomes increasingly more important to achieve high edge steepness in permalloy structures.
As in the case of copper layers, attempts have therefore also been made in permalloy layers to structure these with the assistance of dry etching processes. Precisely in the technology of magnetic heads, however, this presents great difficulties since the permalloy layers to be structured must be executed in relatively thick fashion in this application. Moreover, the relationship of the etching rates of permalloy to conventional photoresists is extremely unfavorable. For this reason, attempts to achieve dry etching of permalloy with the assistance of a photoresist structure directly applied to the permalloy in a photolithographic way have failed. A structuring of permalloy that is still satisfactory for high demands can therefore be implemented with satisfactory results only by use of metallic auxiliary masks. For example, titanium comes into consideration as a material for this mask. This material, however, itself in turn has the property that it cannot be directly structured with the assistance of a photoresist structure generated in a photolithographic way. The only makeshift solution remaining is that further auxiliary masks are employed, so that the structure of a photoresist layer can ultimately nonetheless be transferred onto an uppermost auxiliary mask lying therebelow. The individual auxiliary masks must be dismantled proceeding from above in step-by-step fashion in order to ultimately etch the structure into the first mask lying above the permalloy layer, and in order to be able to finally structure the permalloy layer itself. It is easy to see that the error frequency in such continued etching processes increases enormously. Furthermore, a dimensional tolerance occurs in every etching process, and a sequence of etching processes is hardly capable of proper control given so many process steps. Finally, such a complicated method is also extremely uneconomical. The dry structuring of permalloy layers has therefore not yet been satisfactorily achieved.
The present invention therefore proceeds on the assumption that wet-chemical methods do not meet the demands of progressive developments in the miniaturization of copper line tracks or paths in electronic circuits as well as in thin-film magnetic heads, nor does it meet them in permalloy structures in heads having extremely narrow system heights given relatively thick permalloy layers. For reasons of economy alone, previous solutions for dry etching methods in this field were incapable of proving satisfactory and, over and above this, likewise do not lead to the desired results in qualitative terms.